[gcc r13-1742] lto/106334 - relax assert during WPA tree merging

[Richard Biener]

https://gcc.gnu.org/g:0f129766fdb687394f0eea04f69268b5cc034cda

commit r13-1742-g0f129766fdb687394f0eea04f69268b5cc034cda
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Jul 19 10:02:40 2022 +0200

    lto/106334 - relax assert during WPA tree merging
    
    The dwarf2out map of tree to symbol + offset is populated too early
    when streaming in trees so that when WPA tree merging decides to
    recycle them the mapping prevails and if we are unlucky the same
    address is used for another tree with a symbol + offset DIE to
    record.  The following mitigates the resulting ICE by relaxing the
    assert, allowing re-use of a slot during WPA.  Delaying the register
    would be better but it's already somewhat hairy and uglifying this
    further doesn't look too important right now.
    
            PR lto/106334
            * dwarf2out.cc (dwarf2out_register_external_die): Allow
            map entry re-use during WPA.

Diff:
---
 gcc/dwarf2out.cc | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
index e3920c898f5..3ac39c1a5b0 100644
--- a/gcc/dwarf2out.cc
+++ b/gcc/dwarf2out.cc
@@ -6069,7 +6069,11 @@ dwarf2out_register_external_die (tree decl, const char *sym,
 
   if (!external_die_map)
     external_die_map = hash_map<tree, sym_off_pair>::create_ggc (1000);
-  gcc_checking_assert (!external_die_map->get (decl));
+  /* When we do tree merging during WPA we can end up re-using GC memory
+     as there's currently no way to unregister external DIEs.  Ideally
+     we'd register them only after merging finished but allowing override
+     here is easiest.  See PR106334.  */
+  gcc_checking_assert (flag_wpa || !external_die_map->get (decl));
   sym_off_pair p = { IDENTIFIER_POINTER (get_identifier (sym)), off };
   external_die_map->put (decl, p);
 }